Chicken manure is considered one of the best garden soil amendments. It is high in nitrogen, which encourages plants to develop lots of lush, green growth. (Only rabbit manure is higher in nitrogen.) However, it is so rich that you must use it with care or it will burn roots, scorch seedlings, or make a plant produce lots of leafy growth at the expense of too few fruits.
Adding Manure to the Garden
People who keep a small backyard flock are often willing to give away chicken manure. Even if they have a garden, there is a limit to how much they can use themselves. Some people sell bags of it, and larger poultry farms will sell truckload quantities.
It is best to avoid chicken manure from large farms that keep thousands of chickens confined in cages or large barns. Because of the crowded conditions, these birds are prone to many diseases. Antibiotics and other medications are given with their feed, and may pass into their manure. These medications can have negative effects on you, your garden plants, and anyone who eats that produce.
The best way to use chicken manure is to mix it into an existing compost pile. In the fall, mix dead leaves (carbon) with chicken manure (nitrogen) to form the basis for an excellent compost pile. A good ratio is about one shovelful of manure to every three or four bushels of leaves, roughly mixed. Cover the pile loosely to keep rain out. Turn the pile with a fork once a week for the first month, then monthly after that. After 3 or 4 months, you will have great compost, ready for you to add to your garden.
Chicken manure can be added straight to an empty late-fall or winter garden, because it will break down over the winter. In the spring, it can be dug or tilled in. Use a soil test kit that measures nitrogen so you will be able to judge how much manure to add. This will usually be somewhere between 1 lb. per square foot and 1 lb. per square yard. Bear in mind that nitrogen disappears quickly from soil, so carefully monitor your soil nitrogen level. Do not add fresh manure around existing plants. It is too "hot" and can damage plant roots. It may also force a plant to put up fresh leafy growth at the wrong time---say the fall---when new growth will get zapped by frost.